In recent years, as speeds and volumes of signal transmissions among CPUs in high-end servers, super computers, and the like increase, an optical interconnect technology, which uses lights for close and medium range signal transmissions, is being studied in an attempt to break through limitations of electric signal transmissions. In the optical interconnect, optical transceivers or the like that convert electrical signals to optical signals are provided to perform data transmissions using light signals between optical transmission apparatuses on a transmitting side and a receiving side through transmission channels such as, for example, array optical fibers or the like. For example, a vertical cavity surface emitting laser (VCSEL), which is a small and low power consumption laser device and operable by direct current modulation, can be used as a light signal source for the optical transmission. As an optical receiver, a photodiode (PD) that receives light signals and convert to electrical signals can be used, for example. For example, of the optical transceiver technologies, the following patent documents disclose technologies that control a power consumption based on status of optical transmission apparatus.
Japanese Laid-open Patent Publication No. 2011-044827 discloses a technology for reducing the power consumption of a light emitting element by limiting or stopping a drive current of the light emitting element in response to priority of data to be transmitted when a temperature of an optical transmission apparatus becomes high. Japanese Patent No. 3544932 discloses a technology that reduces the power consumption by reducing a frequency of a tone signal to be transmitted for connection monitoring during a low power consumption mode. Japanese Laid-open Patent Publication No. 2007-013504 discloses a technology for lowering the power consumption by switching to a low speed transmitter circuit and a low speed receiver circuit during a standby mode.
Characteristics of optical elements are known to deteriorate with a temperature increase. More specifically, the characteristics of VCSEL that is a light emitting element of an optical transmission apparatus rapidly deteriorate as the temperature increases, and an operation thereof may stop. In the optical interconnect, it is desirable not to stop a system operation so as not to disconnect the signal transmission even in a range exceeding a given specification temperature (for example, 70-80° C.). To expand an operable temperature range and enable a high-temperature operation at a temperature equal to or higher than the specification temperature, it is effective to suppress the temperature increase by reducing power consumption and reduce a heating effect to the light emitting element. However, when the temperature exceeds the specification temperature (for example, 70-80° C.) that defines stable operations of the light emitting elements, the technologies disclosed by the above three patent documents are unable to continue the stable operation nor expand the operable temperature range of the optical transmission apparatus, and their optical transmission operations become to stop.
A control for reducing the heating effect to the light emitting element is desirable to expand the operable temperature range of the optical transmission apparatus and more specifically to continue the operation at a high temperature exceeding the specification temperature, and implementation thereof is awaited.